As a part of manufacturing electronic components, such as read write heads, for electronic devices, wafers that the electronic components are made out of are electroplated. In order for a electronic component to function properly, the portion of the wafer that the electronic component is made out of must have an appropriate thickness. Manufacturing uses a “specification” to determine what portions of the wafer have the appropriate thickness. Only the portions of the wafer that have the appropriate thickness can be used to make a electronic component out of.
In the conventional process, a wafer is placed in a vat and electric current is passed through the wafer using deflectors associated with a cathode. FIG. 1 depicts a cathode with a wafer associated with on the cathode. The cathode 110 has 8 deflectors d1-d8 for putting current through the wafer 100. A separate current is put through each deflector d1-d8. The 8 regions r1-r8 correspond to the 8 deflectors d1-d8. The wafer 100 has 8 regions r1-r8 for which current for the corresponding deflector d1-d8 affects the thickness of.
A series of wafers are electroplated in a vat one after another. For example, wafer 1 is electroplated, then wafer 2 is electroplated, then wafer 3 is electroplated and so on. The current that is passed through each of the deflectors d1-d8 is adjusted for each wafer that is electroplated in a vat.
The current that is applied to a deflector, such as deflector d3, associated with a new wafer, such as wafer 4, is calculated based on the current that was applied to the same deflector d3 of the previous wafer, e.g., wafer 3, and the thicknesses at the edge of region r3 and the center of the previous wafer. For the sake of illustration, “i” is a variable that designates the deflector. In the case of a wafer that has 8 deflectors, “i” will vary from 1 to 8. Ri is the thickness of the wafer 100's outer edge for the ith region. Rc is the thickness of the wafer 100 at the center 120.
“Old current i” is the current that was applied to the ith deflector for the previous wafer that was electroplated in a vat. The “old current i” is determined based on the current density and the area of the wafer 100 that is plated (also known as “platting area”). A pattern can be used to specify what area of the wafer 100 is plated and what area of the wafer 100 is not platted.
Ri is the thickness of the previous wafer's outer edge at the ith region. Rc is the thickness of the previous wafer's center. The new current i is the current that will be applied to the ith deflector for the next wafer that will be electroplated in the same vat. Therefore, the new current i for the next wafer is equal to a ratio of the thickness of the outer edge (Ri) and the center (Rc) times the old current i of the previous wafer, where i specifies a particular deflector.
The previous wafer is removed from the vat and the thicknesses at the center (Rc) and at the edges (Ri) that correspond to each of the regions r1-r8 are measured manually. An engineer decides whether to change the current that will be applied to the deflectors for the next wafer using the manually measured thicknesses (Rc and Ris) and the currents “i” for the deflectors of the previous wafer.
FIG. 2 depicts the thickness of various portions of a wafer that results from using the conventional process. As can be seen, the thicknesses 210 range from 2.000 to 2.350 for wafer 100. The wafer 100 is thinnest at the center and thickest at the outer edge. The mean of the thicknesses is 2.2328571 and the standard deviation is 0.1470414.
Therefore, there is a need for a way to increase the amount of the wafer that can be used to manufacture electronic components, among other things.